1. Field of the Invention
The present invention relates generally to magnetic heads for reading data written to storage media, and more particularly to magnetic read heads for disk drives.
2. Description of the Prior Art
In recent years there has been a constant drive to increase the performance of hard disk drives by increasing the areal data storage density of the magnetic hard disk. This is done by reducing the written data track width, such that more tracks per inch can be written on the disk. This naturally requires that the width of the read head be reduced so magnetic field interference from adjacent data tracks is not picked up.
Read sensors, of which one type is referred to as a “spin valve”, developed to read trackwidths smaller than 130 nm depend upon the ability to ion mill the sensor to these very small dimensions, and to reliably lift-off the deposited layer materials. A common problem with the fabrication of such small sensors is illustrated in FIGS. 5-15.
The sensor is typically formed of a stack of layers which are generally formed as a region of magnetic material bounded by strips of dielectric or insulating materials. FIG. 5 shows a top plan view of a portion of a wafer 41 as it is being prepared for shaping into a sensor 40. The sensor material region 42 is shown to be bounded by a first dielectric material region 44 and a second dielectric material region 46. These first and second dielectric material regions 44, 46 are chosen to be of non-conducting material. In the prior art, these are preferably chosen to be alumina so that these make up first and second alumina regions 54, 56. A band of masking material 48 such as photoresist is then deposited to protect the material of the sensor material region 42, and first and second dielectric material regions 44, 46 from being cut away during shaping processes such as ion milling. The width of the band of masking material 48 establishes the eventual width of the read head sensor 40 and thus the trackwidth 50. The width of the sensor material region 42 establishes the stripe height 52 of the sensor 40.
The difficulty arises when the exposed portions of sensor material region 42 and first and second alumina regions 54, 56 are subjected to ion milling, since the sensor material 42 and the first and second alumina regions 54, 56 have different milling rates, the sensor material 42 is removed faster than the alumina 54, 56. A series of views of cross-sections of the sensor region 42, as taken through line 6-6 in FIG. 5, and the first alumina region, as taken through line 7-7 of FIG. 5 are shown side-by-side for comparison in FIGS. 6-15. Comparable stages of fabrication of a sensor layer stack 58 in the sensor region 42 are shown in FIGS. 6, 8, 10, 12 and 14, and of an alumina stack 60 in the alumina region 54 in FIGS. 7, 9, 11, 13 and 15 respectively. Since the relative heights of the layers at each stage of fabrication is at issue, the bottom of the sensor layer stack 58 and the bottom of the alumina layer stack 60, are aligned in the pairs of drawings.
In the first stage, FIG. 6 shows the layer of sensor material 62, protective layer 64, preferably of material such as Diamond-like carbon (DLC), and then a layer of masking material 48, and FIG. 7 shows the layer of alumina 66, protective layer 64 and masking material 48.
Next Reactive Ion Etching (RIE) is performed to shape the protective layer material 64 in both FIGS. 8-9.
FIGS. 10-11 show the effect of ion milling, which narrows the sensor material 62 to the dimensions of the mask material 48 and establishes the trackwidth 50. FIG. 11 shows that due to its slower milling rate, the alumina layer remaining 68 may be 200-300 Å thick, as compared to a typical sensor 62 thickness of 400 Å.
FIGS. 12 and 13 show the effects of depositing the hard bias/leads material 70 on both the sensor material region 42, and the first alumina region 54. The hard bias/leads are used to magnetically bias magnetic domains in certain layers of the sensor material 42, and also to supply electric current to the sensor 40. Therefore, in order to maintain the function of the sensor, it is important that the leads are not shorted together. The hard bias/leads material 70 is deposited in a blanketing layer over both the sensor material region 42 and alumina regions 54, 56, (see FIG. 5). In the sensor region 42, the height of the masking material 48 is such that the hard bias/leads material 70 on the masking material 48 is removed vertically far enough from the material 72 deposited on the sides of the sensor that a gap 74 remains, so that three separate elements are formed, namely a first side lead 76 and second side lead 78, and a hard bias/lead material cap 80.
However in the alumina region 54, shown in FIG. 13, since the residual step 68 remains, the hard bias/leads material 70 is raised vertically by this step height 82, as shown by the two set of arrows 82. Consequently, there is not enough vertical displacement of the side leads 76 and the cap 80, so that there is no gap, and side material 72 commonly forms bridges 84 between them. First and second leads 76, 78 are thus no longer electrically isolated, and are thus shorted together.
The next process, shown in FIGS. 14 and 15, is a CMP (Chemical Mechanical Polishing) assisted liftoff. As shown in FIG. 14, this is intended to remove the cap 80 and the masking material 48 from the sensor 62, leaving the first and second leads 76, 78 electrically isolated from each other, except for the conductive path through the sensor 62, as it should be. However, as shown in FIG. 15, in the alumina region 54, the masking material 48 has been unintentionally encapsulated by the hard bias/lead layer 70, which is not removed by the CMP assisted process. Thus this leaves an electrical short between the first and second side leads 76, 78, which must be removed if the sensor 62 is to function properly.
Thus there is a need for a fabrication method which prevents the formation of bridges in hard bias/lead material layer which produces electrical short circuits in disk drive read sensors.